Over at Wasteland and Sky JD Cowan reviews Nightblood and generally likes it, but does spend some time pointing out a trope that was all too common in Vampire fiction of the time:
The "Crucifix only works if you have faith" trope is in this book. It barely features, and I'm sure it was only put in because it was all the rage at the time, but it doesn't change the fact that it makes no sense. It is a misunderstanding of the monster itself. "Faith" has nothing to do with why a Crucifix repels vampires.
The reason the Crucifix.frightens vampires is because Jesus Christ is the Living God who has conquered Death. He is the Blood of Life. He represents the complete opposite of what vampires are, just as Bram Stoker intended, and that is why they cannot stand the sight of what they are not. It is a reminder that they are a mockery of what they wish to be.
It is the same reason they cannot enter any Church: the Church is God's house, it is not the clergy's. They cannot invite vampires in, even if they have weak faith. It isn't up to them. God will never let demons into His House, and can't be tricked like we can. Ironically, this second one is something King got right while everyone up to Joss Whedon keep messing up on even years later.
Nothing in that explanation has anything to do with "Faith", it's about reality. The vampires cannot face the reality of what they are.
This trope is just something tacked to modern stories on because writers wanted to be multicultural and "inclusive", and King wanted to make a statement on the waning faith of the modern world. Those are cute ideas, but that's not as meaningful as the original strength of the Crucifix. If belief is enough to repel vampires then the bullets Stiles believes in should kill every vampire he shoots with it because he believes in his bullets. But they don't. Because this notion doesn't make any sense on a metaphysical level.
However, I don't think it was done this way in Nightblood as any sort of slight. There is no hatred of Christianity or Christians in this book. There is quite a bit of talk about the importance of faith and a purpose in life. One character even quotes scripture before using a Crucifix to burn a vampire's hands off in an important moment. It's just a relic of the sign of the times when one rule was completely misunderstood by the wider culture.
You may recall an earlier post of mine where I lambaste someone's comeback that all I've purchased with a weapon is the illusion of self-defense.
So, in the midst of taking apart the entirety of the King universe(es), Miowara faces the lead vampire from Salem’s Lot – predictably the Count from Sesame Street. He has a cross in his hand, and the count tries to dissuade him from using it, pointing out that the cat is a buddhist, the cross will not work without faith, etc. Miowara uses it anyway, to great effect, and the count asks “why”. Miowara replies that as far as he was concerned, all he knew was that the Count was trying to get him to drop the cross.
Leaving aside the inanity of the "you've only bought an illusion" - there's a reason that armies go to war with guns and not bare hands, and a remarkable consistency to which tyrants render their subjects defenseless first - it points to another fallacy of the whole "cross only works because you believe it" trope. The vampire itself is either wrong about the nature of reality, or, even if he is correct, trying to get you to disarm yourself. In either case, he knows that cross is a threat. One he can perhaps mitigate, but the power it has is very real.
In the case of Miowara, it's very obvious that his lack of faith in God was irrelevant to the effectiveness of the cross, and that the Vampires belief that the cross was powerless without faith in God was also wrong.
Similar to our guns, those who wish us to give up our faith also tell us it's for our own good, to stop wasting our time. It can't help us.
Update - the full quote below, from page 91 of Sword of the Samurai Cat:
"Drop the cross," Johnson said. "You gave your word."
"Under duress," Tomokato said, advancing. "I'm not bound by it."
"Well then," said Johnson, moving to meet him, "I have you now. That cross won't help you. As I said, it's just a symbol. Your faith in Him give it its power. But if you won't face me without it, you obviously don't have any faith, do you? And that cross becomes a mere trinket, doesn't it?"
They halted, facing each other, the vampire towering above Tomakato, gloating down at him, the cat averting his eyes from teh full intensity of Johnson's flaming stare, holding the cross practically in the nosferatu's face.
"Here," Johnson said. "Let me show you."
He snatched at the cross with a taloned hand.
Tomokato held on tightly. "There's something I forgot to mention," he said. "I'm a Buddhist, not a Christian. And all I know is that you were trying to get me to drop this."
Smoke burst through Johnson's fingers. He recoiled with a shriek.